This invention relates to an apparatus for the simultaneous melt extrusion of a plurality of thermoplastic materials to form tubing having a multi-wall structure. More particularly, the invention is concerned with an apparatus for rotatably connecting an extrusion die for making tubing having a multi-wall structure to a series of thermoplastic melt streams exiting from a stationary base or manifold.
The term "thermoplastic material" as used herein is inclusive of all melt-extrudable thermoplastic polymers and compositions containing such polymers in admixture with fillers, pigments, dies, antioxidants, and other additives such as anti-blocking agents, anti-static agents and others ordinarily employed to modify the characteristics of the polymer.
As is known in the art, it is sometimes desirable to rotate an extrusion die in order to distribute any slight non-uniformities more evenly about the extruded tube. This is particularly important when the extruded tube is being internally inflated as it is extruded and while it is yet in the formative plastic state, to a predetermined larger diameter and then circumferentially chilling the tubing at a point to form thin film. However, when conveying a series of thermoplastic streams from a stationary manifold or extruder to a rotating die, the thermoplastic flow through the die is commonly non-uniform. Furthermore, in order to achieve more uniformity of flow, it is desirable for the thermoplastic streams to flow upward in a vertical direction to the extrusion die.